The present invention is directed to a method and apparatus for synchronizing a scan operation. More particularly, the present invention is directed to a method and apparatus for synchronizing a scan operation with the motion of a scan mechanism.
To achieve optimal scan quality, it is desirable to synchronize the motion of a scan mechanism with the scanning operation and the output of the scanning device.
For a stepper-based scan mechanism, the signal that drives the stepper motor may be used to synchronize motion of the mechanism with the scanning operation. This makes it possible to ensure a constant scan rate, if desired.
In contrast, for a DC motor-based scan mechanism, it is desirable to scan based off of the feedback from encoder signals representing the position and velocity of the scan mechanism. In a conventional DC motor-based scan system, an encoder is provided on a shaft of the DC motor. The encoder generates signals each time the drive source rotates by a certain angle. The encoder produces two signal channels, commonly referred to as the channel A phase signal and the channel B phase signal. Edge detectors detect the leading edge and trailing edge of each of the channel A phase signal and channel B phase signal and produce pulses. These pulses are used to synchronize the motion of the scan mechanism with the scan operation.
Several issues arise in synchronizing a scan mechanism using a DC motor with a scan operation. For example, this type of scan mechanism is not guaranteed to move at a constant velocity. Therefore, there is no guarantee that the encoder signals have a constant frequency. Also, the encoder resolution, e.g., counts-per-inch, does not always match the desired scan resolution. This is typically a problem when the encoder resolution is less than the desired scan resolution. The problem is further complicated by the reduced scan speeds of high quality scan modes, during which the scan mechanism is moved at a slower rate of speed.
There is thus a need for a technique for synchronizing the motion of a scan mechanism with a scanning operation that takes into account velocity variations of the scan mechanism.